Previously, there is known an expansion valve, which is applied to a vapor compression refrigeration cycle and depressurizes and expands high pressure refrigerant in such a manner that a degree of superheat of a low pressure refrigerant outputted from an evaporator approaches a predetermined value. This type of expansion valve includes an element portion, which is displaced in response to a temperature and a pressure of the low pressure refrigerant outputted from the evaporator, and a valve element is displaced by the element portion to adjust an opening degree of a throttle passage, which depressurizes and expands the high pressure refrigerant.
More specifically, the element portion includes a diaphragm (a pressure-operated member), which is displaced in response to a pressure difference between an internal pressure of a sealed space and a pressure of the low pressure refrigerant outputted from the evaporator. Here, the sealed space is a space, in which a temperature sensitive medium that changes a pressure thereof in response to a temperature is sealed. The displacement of the diaphragm is conducted to the valve element through a temperature sensitive rod, which conducts the temperature of the low pressure refrigerant outputted from the evaporator.
In this way, the pressure of the temperature sensitive medium in the sealed space is adjusted to the pressure, which corresponds to the temperature of the low pressure refrigerant outputted from the evaporator, and the diaphragm is displaced by the pressure difference between the internal pressure of the sealed space and the pressure of the low pressure refrigerant outputted from the evaporator. Specifically, the diaphragm is displaced in response to the temperature and the pressure of the low pressure refrigerant outputted from the evaporator, and thereby the valve element is displaced to adjust an opening degree of the throttle passage.
In this type of expansion valve, for example, when a response time period (a time constant), which is a time period required to adjust the pressure and the temperature of the temperature sensitive medium into an equilibrium state through the heat conduction from the temperature sensitive rod, is reduced in comparison to a response time period of the other functional component(s) or a response time period of the refrigeration cycle, a phenomenon known as a hunting phenomenon occurs to cause instability of the refrigeration cycle.
In order to address this issue, in a prior art expansion valve, a blind hole is formed in the temperature sensitive rod to extend in an inside of the temperature sensitive rod in an axial direction and to open to the sealed space, and activated carbon is sealed in the inside of the blind hole, or a low heat conductivity layer, which has a lower heat conductivity in comparison to the temperature sensitive rod, is provided to an inner wall of the blind hole (see, for example, the Patent Literature 1). In this way, the required time constant of the heat conduction from the temperature sensitive rod to the temperature sensitive medium is ensured to limit the hunting phenomenon.